1. Field of the Invention
The present invention relates to an optical scanner and an image display apparatus having the optical scanner. For instance, the present invention is suited for a scanner-type image display apparatus for displaying and observing a two-dimensional image by scanning a surface to be scanned with light beams modulated based on image information emitted from light source means or for observing a two-dimensional image by directly introducing light onto eyeballs.
2. Related Background Art
There has been known an image display apparatus that displays an image by scanning the retina of an observer with the aid of light scanning means capable of two-dimensionally scanning light beams modulated on the basis of image information emitted from light source means (e.g., U.S. Pat. No. 5,467,104). U.S. Pat. No. 5,467,104 discloses a technique of scanning red, blue, and green light beams two-dimensionally, that is, horizontally and vertically, and directly forming a two-dimensional image on the retina via an optical system.
Such an image display technique has the following features. Firstly, since each single light beam is scanned to display an image, there is no need to use a display apparatus in which a plurality of pixels are formed in accordance with the required resolution as is the case with an image display apparatus employing a one-dimensional or two-dimensional image display apparatus. Secondly, in principle, no pixel defect is developed.
In realizing an image display apparatus employing such scanning means, a micro electro mechanical system (hereinafter referred to as an MEMS technology) manufactured through a semiconductor process has been known as a light scanning means (e.g., U.S. Pat. No. 5,606,447 and JP H08-334723 A). The light scanning means manufactured by the MEMS technology is lightweight and operable at high speeds. These features are favorable for image display apparatuses. Also, application of the MEMS technology to two-dimensional scanning means for a head-mounted-display apparatus has been known (e.g., SPIE Conference #4407, 19 (June 2001) Wafer Scale Packaging for an MEMS Video Scanner). These light scanning means based on the MEMS technology are designed to tilt a light-reflecting surface through the torsion occurring during resonance of the light-reflecting surface caused by a torsion bar or the like, to thereby deflect and scan light incident on the light-reflecting surface.
On the other hand, there has been known an image display apparatus that displays, on an enlarged scale and in combination with an optical system, an image which is displayed by scanning with light beams modulated on the basis of image information by means of an optical scanner employing a galvanomirror, with the optical scanner and the optical system being positioned with respect to each other with high precision (e.g., Japanese Patent No. 3219465).
To display an image scanned by an optical scanner on an enlarged scale, the optical scanner is generally used in combination with an optical system. However, the combination of the optical scanner and the optical system requires to position with respect to each other very precisely. Under such circumstances, according to an art disclosed in Japanese Patent No. 3219465, a movable mirror surface is arranged parallel to a reference surface on which another mechanical component or the like is attached to the optical scanner. However, the MEMS technology is not used in Japanese Patent No. 3219465. In an optical scanner making use of the MEMS technology, a movable mirror and an optical system must be disposed with respect to each other more precisely. Further, while the optical scanner requires a light source for radiating light beams onto the movable mirror surface, the positional adjustment of the light source also requires precision as a result of downsizing the optical scanner. Accordingly, although burdensome, the positions of the optical scanner and the light source need to be adjusted individually. Furthermore, since an adjustment mechanism must be provided, an apparatus employing the optical scanner cannot be easily downsized.